For semiconductor integrated circuits, a silicon wafer having a prescribed oxygen concentration is required to provide a protection against heavy metal contamination or to improve the various types of quality and the yield, and the silicon single crystal, which is a material for such a silicon wafer, can be manufactured with a single crystal manufacturing apparatus using the Czochralski method (hereinafter referred to as CZ apparatus).
With this CZ apparatus, a raw material for single crystal is filled into a crucible disposed inside a chamber, and inert purge gas is introduced into the chamber, while this raw material is heated and melted with a heater provided outside the crucible. After a seed crystal having thoroughly stuck into this molten melt, the seed crystal is pulled up, while being rotated, in order to grow a single crystal at the lower end of the seed crystal.
Most of the amount of oxygen in the silicon single crystal manufactured by using the above-mentioned CZ apparatus is supplied from the quartz used as the material for the crucible.
In other words, at a contact surface where the silicon melt and the inside surface of the crucible are contacted with each other at high temperature, the quartz (SiO2) in the crucible material always reacts with the silicon (Si) in the melt, and from the crucible surface, volatile silicon oxide (SiO) is eluted into the melt as eluted oxygen. This eluted oxygen is evaporated from the melt surface as volatile SiO, while the eluted oxygen is stirred by the forced convection of the melt due to the rotation of the crucible, the thermal convection due to the temperature distribution in the crucible and the melt in the crucible (hereinafter referred to as temperature distribution in crucible), and the like, a part thereof being transported to the growth interface of the single crystal which is being pulled up, and taken into the single crystal.
By the way, during actual manufacture of the silicon single crystal, the amount of oxygen taken in into the single crystal is complicatedly relates to various manufacturing conditions, such as the SiO reaction speed, the purge gas conditions, the remaining amount of the melt, the heating conditions of the heater, and the like, thus it is considerably difficult to manufacture the single crystal within a prescribed oxygen concentration with a high yield.
Then, conventionally, as the method for controlling the oxygen concentration in a silicon single crystal, the method which pays attention to the relation between the rotational speed of the crucible and the oxygen concentration in the melt; the method which heeds the relation between the pressure, flow rate, flow velocity conditions of the purge gas and the amount of evaporated SiO; the method which pays heed to the applied magnetic field in the crucible and the oxygen concentration in the melt; and the like, have been proposed and implemented.
Further, in the patent literatures 1 to 4, as a promising method for controlling the oxygen concentration that can replace the above-mentioned methods, the method and the apparatus, as outlined below, which use a plurality of heaters to control the above mentioned “temperature distribution in crucible”, thereby controlling the oxygen concentration in the silicon single crystal being pulled up, is disclosed.
Patent literature 1 discloses an apparatus wherein a plurality of heaters are vertically provided in steps along the side periphery of the crucible, and according to the state of progress of single crystal pulling up, electric power is appropriately supplied to each of these heaters, whereby the amount of eluted oxygen and the oxygen elution region are appropriately controlled to hold the oxygen concentration in the single crystal to within a prescribed range. This method features that, during the first half of the single crystal manufacturing process, the melt at the crucible bottom is solidified for a while to control the amount of eluted oxygen from the bottom of the crucible.
Patent literature 2 discloses a method for manufacturing the single crystal having the targeted oxygen concentration with a high yield through suppressing the amount of eluted oxygen at the crucible bottom, by vertically providing a plurality of heaters in steps along the side periphery of the crucible, and maintaining the level of the surface of the melt to within the heating region for the top heater, while setting the ratio of the output of the top heater to that of all the heaters at a prescribed value or higher, and always holding the temperature at the crucible bottom to below the temperature at the crucible upper portion.
Patent literature 3 discloses a method of manufacturing the single crystal using an apparatus having a shield member for finely controlling the oxygen concentration in the single crystal silicon, by independently controlling the outputs of a plurality of heaters provided along the side periphery and the bottom of the crucible, thereby suppressing the high temperature region in the melt from being shifted toward the high temperature side by the above-mentioned shield member.
Patent literature 4 discloses an invention for controlling the oxygen concentration in the silicon single crystal by vertically providing heaters at three-stages along the side of the quartz crucible, varying the electrical resistance for the respective heaters, and supplying electric power to the respective heaters from a common power supply, thereby varying the amount of heat generated in the respective heaters.    Patent literature 1: Japanese Patent Application Laid-Open No. 62-153191    Patent literature 2: Japanese Patent No. 3000923    Patent literature 3: Japanese Patent No. 2681115    Patent literature 4: Japanese Patent Application Laid-Open No. 2001-39792